Ascorbic acid (vitamin C) and other antioxidants, such as α-tocopherol, minimize tissue damage caused by oxidative metabolic processes and also have acceptable biological tolerance. Recently, an ascorbic acid derivative with antioxidant properties, 2-O-octadecylascorbic acid, has been prepared and has been shown to markedly inhibit the myocardial lesions induced by ischemia-reperfusion treatment in rats. Ascorbic acid may also bind to the human serum albumin (HSA) weakly with a binding constant of about 3.5×104 M−1. Ascorbic acid and other antioxidants have been used to stabilize radiopharmaceuticals by decreasing the oxidation of substituents due to radical reactions induced by the decay of the radionuclide.
Metal chelating ligands-are designed for use in Nuclear Medicine, Magnetic Resonance Imaging (MRI), and neutron capture therapy applications. Magnetic resonance (hereinafter sometimes referred to as MR) imaging is widely used for obtaining spatial images of parts of a patient for clinical diagnosis. Typically, the image is obtained by placing the patient in a strong external magnetic field and observing the effect of this field on the magnetic properties of protons contained in and surrounding the organ or tissue of the patient. The proton relaxation times, called T1 or spin-lattice or longitudinal relaxation time, and T2 or spin-spin or transverse relaxation time depend on the chemical and physical environment of the organ or tissue being imaged. In order to improve the clarity of the image, a diagnostic agent is administered intravenously (hereinafter sometimes referred to as I.V.) and is taken up by the organs, such as the liver, spleen, and lymph nodes to enhance the contrast between healthy and diseased tissues.
The contrast agents used in MR imaging derive their signal-enhancing effect from the inclusion of a material exhibiting paramagnetic, ferrimagnetic, ferromagnetic or superparamagnetic behavior. These materials affect the characteristic relaxation times of the imaging nuclei in the body regions into which they distribute causing an increase or decrease in MR signal intensity. There is a need for contrast agents such as those of the present invention, that selectively enhance signal intensity in particular tissue types, as most MR contrast agents are relatively non-specific in their distribution.
Nuclear medicine procedures and treatments are based on internally distributed radioactive materials, such as radiopharmaceuticals or radionuclides, which emit electromagnetic radiations as alpha or beta particles or as gamma rays or photons. Following I.V., oral or inhalation administration, gamma rays are readily detected and quantified within the body using instrumentation such as scintillation and gamma cameras. Compounds derivatized with alpha or beta emitters may be used for radiotherapeutic applications, providing an internal dose of cytotoxic radiation at their target tissues(s).